Generally, if a finger or article touches a specific location of a touch screen, the touch screen checks the location and transfers it to a controller. A terminal equipped with the touch screen outputs various images on the touch screen according to a function demanded by the user and figures out an image touched by the user to perform the corresponding function.
When an input function is performed using a soft keyboard on a touch screen of a smartphone or a tablet PC, a key button is touched to input a letter, and here a broad display area should be ensured since a letter input function and a screen display function should be realized together.
However, in most cases, the soft keyboard occupies about a half of the entire area of the touch screen, and even though the significant area of the touch screen is occupied, each key button is so small to cause touch errors frequently.
In addition, in order to input a word, various key buttons should be pressed on the soft keyboard. However, as the soft keyboard has a greater area, the finger should be moved longer, which consumes much time for input.
Korean Unexamined Patent Publication No. 10-2011-0137128 discloses a letter input method, which is however not available for other languages than Korean, and a user should be acquainted with various input methods in order to input vowels of Korean language.